1. Field of the Invention
The present invention relates to the field of sensor electronics and, in particular, to implantable sensor electrodes and implantable electronic circuits for sensors.
2. Description of Related Art
The development of sensors that can survive for extended periods in less than ideal environments has increased the burden on associated electronics used to obtain and process signals received from such sensors. For example, in the medical device field, physiological parameter sensors are available that may be implanted in vivo and left in an in vivo environment for six months to a year and longer. Such extended lengths of time in an in vivo environment have taxed previously available electronic circuitry used in connection with the physiological parameter sensors.
In addition, the availability of physiological parameter sensors that may be placed in a vascular environment or other environment that may subject a physiological parameter sensor to constant fluid environments has increased the burden on electrodes used in conjunction with a biomolecule that may be part of the physiological parameter sensor. Because multiple electrodes may be used in physiological parameter sensing applications, fluids such as, for example, blood, may create multiple conductive paths across electrodes that compromise the integrity of measurements being made with the electrodes. Electrode configuration and associated circuitry known up to this point have been ill-equipped to handle the demands of such an environment.
Moreover, the extended periods of time in which a physiological parameter sensor may be implanted in vivo have placed extra demands on the power sources driving the sensor electrodes and sensor electronics. For example, previous sensor technology, which may have been designed for relatively short term in vivo implantation of a sensor, may have included a power source, such as, for example, a lithium battery, for in vivo implantation along with the sensor. Such short term sensors may have been designed, for example, for emergency use in surgical applications where the intent was to keep the sensor powered even in storage. Thus, a hospital could store the sensors, implant them during emergency surgery, and expect to get sensor readouts immediately. However, with the advent of sensors for long term in vivo implantation, storing a sensor with an activated power source may deplete the power source to such an extent that using the sensor for long term in vivo implantation may be impractical and even unadvisable.
In addition, the demand for enhanced in vivo signal processing has put even greater demands on an already overburdened in vivo power source. Implantable, in vivo automated systems require not only extended term power requirements for powering an implanted power sensor, but also require increased power availability for the circuitry used to obtain and process sensor signals.
Embodiments of the present invention relate to sensor electrodes and sensor electronics interfaced to the sensor electrodes.
Embodiments of the present invention include an electronic circuit for sensing an output of a sensor including at least one electrode pair for sensing a parameter. The at least one electrode pair may have a first electrode and a second electrode, wherein the first electrode wraps around the second electrode. The electronic circuit may contain circuitry for processing the parameter. The parameter sensed by the electrode pair may be a physiological parameter such as, for example, glucose or oxygen.
The first electrode may wrap around the second electrode in a U-shaped fashion or may surround three sides of the second electrode. The layout of the first electrode and a second electrode may be such that it minimizes cross coupling between the first electrode and the second electrode.
The electronic circuit may include a reference electrode for setting a reference voltage for the at least one electrode pair. The reference voltage may be set to about 0.5 volts.
In addition, the circuitry may include a line interface for interfacing with input/output lines; a rectifier in parallel with the line interface; a counter connected to the line interface; and a data converter connected to the counter and the at least one electrode pair. Control logic may be connected to the counter and the line interface. The control logic may include a state machine and a state decoder connected to the state machine. The control logic may include a microprocessor.
In the electronic circuit, the rectifier may transfer power from communication pulses to a capacitor. The capacitor may power the electronic circuit using power stored from the communication pulses.
The data converter may be an analog-to-digital converter, a voltage-to-frequency converter, or a current-to-frequency converter. If the data converter is a current-to-frequency converter, an output of the current-to-frequency converter may be scaled using a prescaler before connecting to the counter. The prescaler may be a divide-by-16 prescaler.
The circuitry may also include a temperature sensor for reading a temperature of an environment and a voltage reference for applying a voltage to a reference electrode. In addition, switched capacitor circuits may be used as resistors in the electronic circuit.
These and other objects, features, and advantages of embodiments of the invention will be apparent to those skilled in the art from the following detailed description of embodiments of the invention when read with the drawings and appended claims.